1. Field of Endeavor
The present invention relates to a method for operating a gas turbine, and to a gas turbine. In particular, the invention relates to a gas turbine whose flue gases are partly recirculated and partly fed to a CO2 capture plant.
2. Brief Description of the Related Art
FIG. 1 shows an example of a power plant having a sequential combustion gas turbine 1 including a compressor 2 that feeds a combustion device 3, in which a fuel 13 is injected and combusted forming hot gases that are expanded in a high pressure turbine 4; the flue gases from the high pressure turbine 4 are fed into a second combustion device 5 in which further fuel 15 is injected and combusted, forming hot gases that are further expanded in a low pressure turbine 6.
The flue gases from the low pressure turbine 6 are supplied into a heat exchanger 7 to supply energy to a steam turbine plant 8.
After having passed through the heat exchanger 7, the flue gases pass through a cooler where they are cooled to be then introduced into a diverter 9, where a first flue gas flow is diverted into a mixer 10 to be mixed with fresh air to form a mixture that is fed to the compressor 2.
From the diverter 9 a second flue gas flow is diverted into a CO2 capture plant 11.
This power plant lets the CO2 emissions be controlled and reduced, but in some cases, it may cause different drawbacks.
In fact, since the combustion devices operate with an oxidizer (being the mixture of recirculated flue gases and fresh air) having a lower oxygen concentration than fresh air, during operation the flame stability is reduced when compared to the flame stability of combustion devices operated with fresh air.
This may cause pulsations and increase the blow out temperature, so reducing the operational flexibility; in addition, the unburned hydrocarbon and CO emissions may also increase, in particular at part load operation.